It is known that mono-1-olefins (α-olefins), including ethylene, can be polymerized with catalyst compositions employing titanium, zirconium, vanadium, chromium, or other metals, often combined with a solid oxide and in the presence of cocatalysts. These catalyst compositions can be useful for both homopolymerization of ethylene, as well as copolymerization of ethylene with comonomers such as propylene, 1-butene, 1-hexene, or other higher α-olefins. Therefore, there exists a constant need to develop new methods of making and using olefin polymerization catalysts.
An example of this need is seen in the manufacture of bridged or ansa-metallocene catalysts. In general, ligands for ansa-metallocenes are prepared by following a multi-step synthesis. Clearly, it would significantly reduce metallocene preparation cost if the synthetic approach of the corresponding ligands could be simplified. Alt et al., J. Organomet. Chem. 1998, 568, 87-112 (Alt et al.), which is incorporated herein in its entirety by reference, reported a synthesis method for the ligands for certain ansa-metallocenes. The greatest advantage of this method is that fewer synthetic and isolation steps are employed as compared to the multi-step approach. In addition, it is more convenient to prepare different analogs with different substituents on the cyclopentadienyl ring via the one-pot synthesis. Unfortunately, the method described by Alt et al. does not readily produce ligands of the form C13H8—CR1R2—C5H3R3, where R1 and R2 are phenyl or substituted phenyl, R3 is alkyl, alkenyl, or substituted silyl. Thus, there exists a need for a one-pot synthesis for such ligands in the manufacture of metallocenes. Accordingly, the present invention is directed to that need.